ZOOLOGY AND EOT AN Y, MICROSCOPY^ ETC. 507 



Mayer's Dissecting' Microscope. — This (fig. 93) is one of the most 

 convenient dissecting Microscoi3es which we have yet seen. 



The stage consists of a large metal frame, 10 cm. square, to which 

 are attached folding wooden supports for the hands. For minute 

 objects a metal plate is dropped into the frame, in which is a small 

 central opening, which can be closed by either a black or white disc 

 as desired. For larger objects, especially living aquatic animals, the 

 metal plate is replaced by glass, and white or black plates can be 

 brought beneath it, according to the background required. These 

 plates are turned away from the stage by the milled heads shown in 

 front of the stage on the right. 



There are three arms for lenses. The lower one shown in the fig. 

 is for high powers (the upper being removed), while the upper is for 

 Zeiss's aplanatic lenses ( X 6 and 10). By the combination of the 

 movements of the two arms the lenses can be made to traverse all 

 parts of the stage. An extra holder is also supplied for the high 

 powers, which can be moved in the same way over the whole stage. 



Magic Lantern v. Microscope.* — ^Mr. T. King considers that 

 for purposes of general teaching the magic lantern possesses the 

 advantage over the Microscope of lessening both labour and expense. 

 By means of micro-photography, the magnified image of minute 

 objects, such as sections of vegetable tissues, diatoms, &c., can be 

 photographed in a form available for use as a lantern-slide. With 

 the aid of such slides, the teacher can at once explain to the whole 

 class what can only with the Microscope be explained individually. 



InostranzefFs Comparison Chamber for the Microscopical Study 

 of Opaque Minerals and other objects.f — M. A. Inostranzeff writes 

 as follows : — 



" The great importance of the Microscope in the study of rocks 

 cannot be denied. To the Microscope we owe the modern classifica- 

 tion of rocks, our knowledge of the structure of the rocks themselves, 

 of the minerals which compose them, and of their inclusions, as well 

 as of many modifications and metamorphoses to which rocks and 

 minerals are subject. Up to the present time, however, scarcely any 

 progress has been made to a rational method of investigating the 

 opaque minerals which enter into the composition of rocks. Ten 

 years ago I published | a note on the study of opaque minerals, in 

 which I proposed to employ the colour and lustre of these minerals 

 to distinguish between them. By means of brilliant illumination 

 from above, little differing from ordinary daylight, the lustre and 

 colour may be made evident. In this way I succeeded in determining 

 eight opaque minerals in the rocks of the district of Olonez, and in 

 showing, in several cases, their genetic relations. But the determina- 

 tion of colour and lustre being liable to subjective errors, I have 



* Pioc. and Trans. Nat. Hist. Soc. Glasgow, i. (1886) p. xxx. 

 t Comptes Kendus, c. (1885) pp. 1396-8. Neues Jahrb. f. Mineral., ii. 

 (1885) pp. 94-6 (2 figs.). 



t Abh. d. Moskaiier Naturforschergesellschaft, vi., Part 1. 



2 L 2 



